<div class="dropdown" id="dropdown">
    <button class="btn btn-primary"  data-toggle="dropdown">
        下拉菜单
        <span class="caret"></span>
    </button>
    <ul class="dropdown-menu">
        <li><a href="#">首页</a></li>
        <li><a href="#">咨询</a></li>
        <li><a href="#">咨询</a></li>
        <li><a href="#">关于</a></li>
    </ul>
</div>